Effects of irradiance, temperature and water availability on respirati
on and photosynthesis in a maritime Antarctic liverwort, Marchantia be
rteroana, were investigated. Carbon dioxide exchange was measured usin
g an infra-red gas analysis system under controlled conditions. The re
lationships between respiration, photosynthesis, irradiance and temper
ature were modelled. Application of these models to year-round micro-c
limate data provided an estimate of yearly net productivity of 823 (SE
= 75) mg C . g(-1) ash-free dry weight. year(-1); this is somewhat hi
gher than figures obtained for other Antarctic cryptogams. Desiccation
had a highly adverse affect on Marchantia. Photosynthetic capacity wa
s reduced below a water content of 12 g . g(-1) afdw. and there was on
ly a limited recovery (ca. 10%) after dehydration. Freezing also cause
d a great reduction in photosynthesis, although the model suggested th
at photosynthesis at sub-zero temperatures is likely. It is suggested
that seasonality in the photosynthetic capacity and the survival of su
bzero temperatures might be important. It is concluded that Marchantia
is a relatively productive Antarctic cryptogam that may dominate favo
urable areas, but that its low tolerance of environmental stress, part
icularly desiccation, limits its distribution to relatively mild habit
ats.